#!/usr/bin/env python3
"""Convert paired metadata.tsv -> metadata_shard.jsonl (s-s training format).

Input TSV (header required, tab-separated):
    zh_path  en_path  zh_text  en_text  category

Output JSONL: one JSON object per line, schema:
    {
      "task_type": "s-s",
      "conversation": [
        {"role":"user", "message_type":"text",  "content": <prompt>},
        {"role":"user", "message_type":"audio", "content": <src_wav_path>},
        {"role":"assistant", "message_type":"audio-text",
         "content": [<tgt_wav_path>, <tgt_text>]}
      ]
    }

Each TSV row produces 2 conversations by default (en->zh and zh->en),
matching the original metadata_shard distribution.

Usage:
    python tsv_to_metadata_shard.py metadata.tsv -o metadata_shard.jsonl
    python tsv_to_metadata_shard.py metadata.tsv --directions en2zh   # only one
    python tsv_to_metadata_shard.py metadata.tsv --shard-size 50000   # split
"""
import argparse
import csv
import json
import os
import sys

EN2ZH_PROMPT = ("Translate the given English speech into Chinese "
                "while preserving its expressiveness.")
ZH2EN_PROMPT = ("Translate the given Chinese speech into English "
                "while preserving its expressiveness.")


def make_conversation(prompt: str, src: str, tgt: str, tgt_text: str) -> dict:
    return {
        "task_type": "s-s",
        "conversation": [
            {"role": "user", "message_type": "text", "content": prompt},
            {"role": "user", "message_type": "audio", "content": src},
            {"role": "assistant", "message_type": "audio-text",
             "content": [tgt, tgt_text]},
        ],
    }


def open_writer(out: str, shard_size: int):
    """Yield writer fn that handles optional sharding."""
    if shard_size <= 0:
        f = sys.stdout if out == "-" else open(out, "w", encoding="utf-8")
        def write(obj):
            f.write(json.dumps(obj, ensure_ascii=False) + "\n")
        def close():
            if f is not sys.stdout:
                f.close()
        return write, close

    base, ext = os.path.splitext(out if out != "-" else "metadata_shard.jsonl")
    if not ext:
        ext = ".jsonl"
    state = {"idx": 0, "count": 0, "f": None}

    def _rotate():
        if state["f"] is not None:
            state["f"].close()
        path = f"{base}_{state['idx']:03d}{ext}"
        state["f"] = open(path, "w", encoding="utf-8")
        state["count"] = 0
        state["idx"] += 1

    _rotate()
    def write(obj):
        if state["count"] >= shard_size:
            _rotate()
        state["f"].write(json.dumps(obj, ensure_ascii=False) + "\n")
        state["count"] += 1
    def close():
        if state["f"] is not None:
            state["f"].close()
    return write, close


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("tsv",
                    help="metadata.tsv (header: zh_path,en_path,zh_text,en_text,category)")
    ap.add_argument("-o", "--out", default="metadata_shard.jsonl",
                    help="output path; '-' for stdout (default: metadata_shard.jsonl)")
    ap.add_argument("--directions", default="both",
                    choices=["both", "en2zh", "zh2en"])
    ap.add_argument("--shard-size", type=int, default=0,
                    help="if >0, split output into <out>_NNN.jsonl shards of this many lines")
    args = ap.parse_args()

    write, close = open_writer(args.out, args.shard_size)

    required = {"zh_path", "en_path", "zh_text", "en_text", "category"}
    n = 0
    with open(args.tsv, encoding="utf-8", newline="") as f:
        reader = csv.DictReader(f, delimiter="\t")
        missing = required - set(reader.fieldnames or [])
        if missing:
            sys.exit(f"missing TSV columns: {missing}")

        for row in reader:
            if args.directions in ("both", "en2zh"):
                write(make_conversation(
                    EN2ZH_PROMPT, row["en_path"], row["zh_path"], row["zh_text"]))
                n += 1
            if args.directions in ("both", "zh2en"):
                write(make_conversation(
                    ZH2EN_PROMPT, row["zh_path"], row["en_path"], row["en_text"]))
                n += 1

    close()
    print(f"wrote {n:,} conversations", file=sys.stderr)


if __name__ == "__main__":
    main()